Liquid crystals are substances that exhibit physical properties between those of a conventional liquid and those of a crystal. Similar to fluids, the molecules in liquid crystals are free to diffuse about their positions. However, the molecules in the liquid crystals tend to maintain a small degree of long range orientational, and sometimes positional, order. As such, liquid crystals are anisotropic, as is typical of crystals.
A vast array of organic and metal-containing substances exhibit liquid crystallinity. A common feature of these molecules is either an elongated or flattened, somewhat inflexible molecular framework which is usually depicted as being either cigar- or disc-shaped. The orientational and positional order in a liquid crystal phase is only partial, with the intermolecular forces striking a very delicate balance between attractive and repulsive forces. As a result, liquid crystals display an extraordinary sensitivity to external changes in a physical system (e.g., temperature, pressure, electric and magnetic fields, shearing stress or foreign vapors).
Biological and chemical sensing at low concentration levels is of extreme importance for environmental monitoring and bio-defense. In view of the foregoing, it has been contemplated to utilize liquid crystals as a sensing element. By way of example, Abbott et al., U.S. Pat. No. 6,852,285, discloses a device for detecting an interaction between an analyte and a recognition moiety of a liquid crystal. The device includes a first substrate having a surface and a second substrate having a surface. The first substrate and the second substrate are aligned such that the surface of the first substrate opposes the surface of the second substrate. A first organic layer is attached to the surface of the first substrate. The organic layer includes a first recognition moiety which interacts with the analyte, and a mesogenic layer between the first substrate and the second substrate. The mesogenic layer includes a plurality of mesogens. At least a portion of the plurality of mesogens undergoes a detectable switch in orientation upon interaction between the first recognition moiety and the analyte. Preferably, the substrate lo of the device is a mesh, for example, a transmission electron microscopy (TEM) grid. As such, the recognition moiety can be attached to the spaces between the mesh members (i.e., in wells) and the mesogenic layer is floated on the top of the substrate.
While functional for its intended purpose, the method disclosed in the '285 patent requires careful manual operation to fill and stabilize the liquid crystal film in the grid. This, in turn, inhibits the use of the liquid crystal sensing method in industrial or field operations. Therefore, it can be appreciated that creating a stable and reusable liquid crystal sensing element would be highly desirable.
It is a primary object and feature of the present invention to provide a microfluidic device integrating a liquid crystal sensing element that allows for the automatic formation of a sensing interface.
It is a further object and feature of the present invention to provide a microfluidic device integrating a liquid crystal sensing element that allows for better control of the interaction between a target phase and the liquid crystal.
It is a still further object and feature of the present invention to provide a microfluidic device integrating a liquid crystal sensing element that is simple to use and inexpensive to manufacture.
In accordance with the present invention, a sensing device is provided for sensing a target. The sensing device includes a body having a first inner surface at least partially defining a channel network for receiving the target therein. A liquid crystal is anchored to the first inner surface of the body and includes a plurality of mesogens. Each mesogen is movable between a first orientation and a second orientation in response to lo communication with the target.
The sensing device includes a first binding layer for anchoring the liquid crystal to the first inner surface. The first binding layer is fabricated from gold. The body may also define a second inner surface axially spaced from the first inner surface. The second inner surface at least partially defines the channel network and the liquid crystal is also anchored to the second inner surface of the body. A second binding layer, e.g. fabricated from gold, anchors the liquid crystal to the second inner surface.
The channel network in the body includes a first channel and a second channel. The first and second channels communicate with each other. The first channel includes an input and an output, and is partially defined by the first inner surface. The second channel also includes an input and an output. The second channel is partially defined by a channel wall which is hydrophilic. The channel wall is adjacent the liquid crystal anchored to the first inner surface of the first channel.
In accordance with a further aspect of the present invention, a sensing device is provided for sensing a target in an aqueous solution. The sensing device includes a body defining a first channel for receiving the aqueous solution. The first channel has an input and an output. A liquid crystal communicates with the first channel and includes a plurality of mesogens. Each mesogen is movable between a first orientation and a second orientation in response to communication with the target.
The first channel is partially defined by a first inner surface and the sensing device further includes a first binding layer for anchoring the liquid crystal to the first inner surface. It is contemplated for the first binding layer to be fabricated from gold. The first channel may also be partially defined by a second inner surface axially spaced from the first inner surface. The second inner surface at least partially defines the first channel. The liquid crystal is also anchored to the second inner surface of the body by a second binding layer. The second binding layer is fabricated from gold.
Alternatively, the body may also define a second channel. The first and second channels communicate with each other. The second channel is partially defined by an inner surface and the liquid crystal is anchored to the inner surface. In such embodiment, the first channel is partially defined by a channel wall that is hydrophilic. The channel wall is adjacent the liquid crystal anchored to the inner surface of the second channel.
In accordance with a still further aspect of the present invention, a method of sensing a target in an aqueous solution is provided. The method includes the step of flowing the aqueous solution into a first channel of a microfluidic device such that the aqueous solution communicates with a liquid crystal. A plurality of mesogens in the liquid crystal reorientate in response to communication between the plurality of mesogens with the target in the aqueous solution.
The liquid crystal may be anchored to a surface defining a second channel in the microfluidic device. The second channel communicates with the first channel and the first channel is partially defined by a hydrophilic surface. The step of anchoring the liquid crystal to the surface includes the step of providing a bonding layer, e.g. gold, between the surface and the liquid crystal. The orientation of the plurality of mesogens is monitored to determine the presence of the target in the aqueous solution.